From clearing out dead leaves and trees, to jump-starting new growth, to returning minerals to the soil, forest fires have many benefits. However, with increasing temperatures and droughts predicted with upcoming climate changes, it may be difficult for some plants to regenerate after forest fires.

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According to researchers from Oregon State University, moisture stress is a key limitation for conifer regeneration following major forest fires that occur on dry, low-elevation sites. As a result, reforestation post-fire recovery on dry sites may be slow and uncertain.

The study was conducted in the eastern Cascade Range of Oregon, which prior to a 2002 fire was mostly ponderosa pine with some Douglas-fir and other tree species.

"A decade after this fire, there was almost no tree regeneration at lower, drier sites," said Erich Dodson, a researcher with the OSU Department of Forest Ecosystems and Society. "There was some regeneration at higher sites with more moisture. But at the low elevations, it will be a long time before a forest comes back, if it ever does."

Unfortunately, similar situations may be found in many areas of the American West in the future and recruitment of new forests may be delayed or prevented. While mature trees can use their roots to tap water deeper in the soil, competition with dense understory vegetation can make it difficult for seedlings to survive.

Openings in ponderosa pine forests created by wildfire have persisted for more than a century on harsh, south-facing slopes in Colorado, the researchers noted in their report. And fire severity is already increasing in many forests due to climate change — what is now thought of as a drought in some locations may be considered average by the end of the next century.

If trees do not regrow, there will be many implications for the forest ecosystems including reducing carbon storage and wildlife habitat while amplifying the greenhouse effect.

Restoration treatment including thinning and prescribed burning may help reduce fire severity and increase tree survival after wildfire, as well as provide a seed source for future trees, Dodson said. These dry sites with less resilience to stand-replacing fire should be priorities for treatment, if maintaining a forest is a management objective, the study concluded.

The study also reports that higher-elevation, mixed conifer forests in less moisture-limited sites may have a better chance of recovering from stand-replacing wildfire compared to the lower-elevation forests.